Hi Stephen,
The group was called the Milang Historic Steam & Shipping Museum. Milang is a town on Lake Alexandrina. The president was David Dunk. The last I knew (about a decade ago) David was in Murray Bridge. You might have more luck locating Dick Love who was one of the senior members of the group. He was living in Meningie on the other side of the lake.
The Invincible was owned by the Dunk & Love families and was on loan to the museum. What's left of her is still sitting in a paddock at Milang, along with sections of the Koondrook barge.
I think the group just fizzled out. They couldn't generate new interest and community support & there were only a limited number of people putting in the hours. They also took on a huge task. As people's lives changed they weren't able to commit to the group, so it died.
I'm Mac btw. Rude of me not to introduce myself.
The following are scans of previous pictures I have posted as well as some google earth/streetview photos of the site. The steel sections are the Koondrook & the piles of old timber are the Invincible. I think the new timber was donated to the group for restoration. I'm assuming that the stacks of steel on the right are the sides of the Koondrook. The Invincible's iron frames must be somewhere.